The invention relates to a photochromic composition, and more particularly to an organic photochromic composition comprising spiro[indoline-2,3'-[3H]-naphth[2,1-b][1,4]oxazine] (SO) dye and an uncoventional ultraviolet (UV) stabilizer.
Compounds which undergo reversible photo-induced color changes are termed photochromic compounds. When subjected to ultraviolet light or visible irradiation, these photochromic compounds change their transmission. They subsequently revert to their original color state when they are subjected to a different wavelength of radiation or the initial light source is removed.
Although the organic photochromic materials have been known for over 50 years, they have not had widespread industrial or commercial use. This is primarily due to the irreversible decomposition phenomenon, generally known as light fatigue. Repeated exposure to light cause the photochromic materials to lose their photochromism.
It is thought that light or heat or both light and heat are responsible for the photodecomposition of organic photochromic compounds. Thus, many people have tried to increase the light fatigue resistance of the compounds by adding numerous conventional antioxidants or ultraviolet light absorbers. For example, U.S. Pat. No. 3,212,898 teaches the use of conventional UV absorbers such as benzophenone and benzotriazole to increase the photochromic life of photochromic benzospiropyran compounds. Similarly, U.S. Pat. No. 3,666,352 teaches the use of conventional UV light absorbers in photochromic mercury thiocarbazonate lenses, transparent to radiation of wavelengths greater than 4200 Angstrom units and opaque to radiation of wavelengths less than 4200 Angstrom units, in order to substantially increase the durability of the lenses towards photochemical degradation.
One class of organic photochromic compounds, spiro[indoline-2,3'-[3H]-naphth[2,1-b][1,4]oxazine] (SO) dyes are known to have good light fatigue resistance. This class of photochromic compounds has been disclosed in U.S. Pat. Nos. 3,562,172, 3,578,602, and 4,215,010. Although a photochromic article or lens made from this class of compounds shows excellent light fatigue resistance as compared to one made from other photochromic compounds, further improvement of the light fatigue resistance is desirable in order to broaden the use of the photochromic article and to increase its useful lifetime. SO dyes with improved light fatigue resistance would have a particular utility in fabricating photochromic sunglasses, opthalmic lenses, ski goggles, window coatings and the like.
The precise mechanism for photodecomposition of SO dye is not yet fully understood. Although some circumstantial evidence indicates that oxygen is involved in the photodecomposition process, the traditional antioxidants (hindered phenols and amines) do not improve the light fatigue resistance of SO dyes. The conventional UV stabilizers, substituted benzophenones and benzotriazoles, cause a small improvement in the light fatigue resistance of SO dyes, but they cannot be used effectively since they create a screening effect by absorbing UV radiation strongly in the region where the SO dyes absorb UV radiation. By competing with the SO dyes to absorb UV light, these conventional stabilizers subsequently decrease the effective light intensity for SO dye activation. Furthermore, some of the conventional UV stabilizers are detrimental to SO dyes under certain conditions.
Accordingly, it is a principal object of the present invention to improve the light fatigue resistance of an organic photochromic composition containing SO dye.
It is another object of the present invention to improve the light fatigue resistance of these photochromic compositions without hindering their photocolorability.
It is a further object of the present invention to use such improved photochromic compositions to fabricate photochromic articles such as sunglasses, opthalmic lenses, ski goggles, window coatings and the like.